On Thu, May 30, 2024 at 07:16:56PM -0700, Eric Biggers wrote:

On Thu, May 30, 2024 at 06:03:18PM -0700, Ross Philipson wrote:

quoted

From: "Daniel P. Smith" <redacted>

For better or worse, Secure Launch needs SHA-1 and SHA-256. The
choice of hashes used lie with the platform firmware, not with
software, and is often outside of the users control.

Even if we'd prefer to use SHA-256-only, if firmware elected to start us
with the SHA-1 and SHA-256 backs active, we still need SHA-1 to parse
the TPM event log thus far, and deliberately cap the SHA-1 PCRs in order
to safely use SHA-256 for everything else.

The SHA-1 code here has its origins in the code from the main kernel:

commit c4d5b9ffa31f ("crypto: sha1 - implement base layer for SHA-1")

A modified version of this code was introduced to the lib/crypto/sha1.c
to bring it in line with the SHA-256 code and allow it to be pulled into the
setup kernel in the same manner as SHA-256 is.

Signed-off-by: Daniel P. Smith <redacted>
Signed-off-by: Ross Philipson <redacted>

Thanks.  This explanation doesn't seem to have made it into the actual code or
documentation.  Can you please get it into a more permanent location?

I see that a new version of the patchset was sent out but this suggestion was
not taken.  Are you planning to address it?

- Eric